Phase shifter



May 31, 1960 UNDI-EY, JR 2,939,084

PHASE SHIFTER Original Filed Nov. 30, 1954 Patented May 31, 1960 PHASESHIFTER Original application Nov. 30, 1954, Ser. No. 471,987.

Divided and this application May 1, 1958, Ser. No- 732,347

6 Claims. (Cl. 328-155) This invention relates to phase shifter circuitsand especially to circuits capable of producing large shifts in phase asrequired by certain applications in which phase shifters are employed.An example of one application of a phase shifting circuit arranged inaccordance with this invention is shown in my pending application SerialNo. 471,987, filed November 30, 1954, of which this application is adivision. In that application, a phase shifting circuit is required inorder to control the location of visual images representing simulatedreturn echo signals on the scope of sonar equipment employing a fourquadrant transducer system. The relative phases of the echo signal ineach transducer channel provided for each quadrant are responsive to thetrain and tilt angle error and target aspect signals generated by thetrainer. Because the phase shifter circuit is designed for that specialapplication, a limiter circuit is associated with it which serves tolimit the modulating or phase shifting voltage to that which wouldproduce plus and minus 90 phase shifting corresponding to the full gridswing of the tubes in the phase shifter circuit from cut off to zerobias as the circuit has been so adjusted. When these circuits areassociated with the sonar gear, it is important that the grid swing ofthe phase shifter tubes should be limited so that the phase shiftingdoes not exceed plus and minus 90 as otherwise the associated sonar gearwould begin to repeat the target display. However, it is preferable thata limit be placed upon the phase shifter grid swing in any case so as toprevent excessive phase modulation.

One object of the invention is to provide a relatively simple phaseshifting circuit capable of large phase shifts with a minimum ofamplitude modulation.

Another object of the invention is to provide a phase shifting andlimiter circuit especially arranged to prevent the output from beingovershifted in the plus and minus directions.

One advantage of the circuit arrangement as contemplated by theinvention is that it may be operated to produce a relatively largelinear phase swing with only a limited amount of amplitude variation.Moreover, this is accomplished with a high degree of reliability andstability and with a minium of circuit complexity as compared withpresently existing phase shifting circuits. Other advantages and objectsof the invention may be appreciated on reading the following detaileddescription which is taken in conjunction with the drawing which is aschematic of the phase shifting and limiting circuit.

As shown in the drawing, there is provided a specially arrangedresistive source for supplying D.C. control voltages to a four channellimiter and phase shifting circuit. In accordance with the illustratedarrangement, the control voltage source comprises a diamond shapearrange ment of eight equal resistors With two to a side. While thephase shifting circuit hereinafter described is not limited in itsapplication to a sonar training device, the employment of the fourchannels will be explained in that context. In this connection, it mustbe understood that the channels serve to carry simulated echo signals toa four quadrant transducer system of the associated sonar gear.Accordingly, one of the four channels represents the bottom lefttransducer channel, another the bottom right transducer channel, thethird channel represents the top right transducer channel, the fourthchannel being the top left transducer channel. Resistors 1 and 2 of thediamond shape resistor arrangement are connected to the bottom leftchannel; resistors 3 and 4 are connected to the bottom right transducerchannel; resistors 5 and 6 are connected to the top right transducerchannel and resistors 7 and 8 to the top left transducer channel. Theintermediate D.C. biases from the junctions of the two resistors on aside are fed to the corresponding limiter and phase shifter channels.The left and right points of the diamond are fed with the left and righterror bias voltages and the top and bottom points are fed with the topand bottom error bias voltages from sources (not shown). Connected tothe left hand inputs in advance of the phase shifters are capacitors 9and 10. To the right hand inputs are connected capacitors 11 and 12.Through capacitors 9 and 10 an AC. control voltage is introduced to theleft hand limiter phase shifter channels and another signal of equal andopposite polarity is introduced through capacitors 11 and 12 into theright hand limiter phase shifter channels. The capacitor connections inno way disturb the biases since the capacitors cannot pass D.C. andtherefore produce loading. At the same time the resistors havesufiicient impedance so that the A.C. source is not excessively loaded.The circuit is actually similar to a resistance capacitor coupling ascommonly employed in audio amplifiers.

The limiters circuit which receives the four control voltages from thediamond shape resistive network con- .sists of a diode in series withthe grid of a cathode follower in each channel. For example, diode 13and cathode follower 14 are so connected in the top left channel; diode15 and cathode follower 16 are so connected in the top right channel;diode 17 and cathode follower 18 are likewise connected in the bottomright channel and diode 19 and cathode follower 20 are connected as suchin the bottom left channe The diodes 13, 15, 17 and 19 have their platesconnected to the cathode follower grids in the above arrangement withgrid leak resistors 21, 22, 23 and 24, respectivley, in each combinationtying the cathode follower grids to ground reference.

The action of the limiter circuits can be explained in the followingmanner. Consider first a signal excursion in the positive direction.This naturally carries the cathode of the diode with it and since theplate of the diode is at ground the diode ceases to conduct when thecathode reaches this potential. This opens the diode circuit and morepositive signal swings cannot be passed on to the cathode follower grid.Thus the positive signal swing limit obtainable from the cathodefollower is set. If signal swings in the negative direction are nowconsidered we see that the diode will still continue to conduct carryingthe diode plate and cathode follower grid along with it. Eventually thecathode follower will be cut oif by its grid becoming sufficientlynegative. This therefore sets the negative clipping level limit.

The voltage limit level out of the cathode follower will therefore bezero volts for the negative swings and a positive limit on positiveswings determined by the positive bias on the plate ofthe diode. Thispositive voltage at the cathode of the cathode follower will be thepositive limit. It should be noted that this can be adjustedindependently of the input signal by the choice of cathode followerplate voltage and/or cathode resistor value as well as the bias on theplate of the diode. It will also be noted that the D.C. bias voltageshave been offset and this, it will be seen, is necessary for fittingproperly the phase shifter grid swing characteristics. This particulararrangement and adaptation. of the limiter circuit is conditioned by theparticular nature and requirements of the specific application of thephase shifter circuit.

As shown in the drawings,- a. dual triode tube is provided for, eachofthe four channels. One triode section of the tubescomprises triode phaseinverters 25, 26,. 27 and 28 and the other triode section comprisestriode phase shifters 30, 31, 32 and 33. The phase inverters have equalload resistors in the plate and cathode. The phase shifter tubes, havetheir plates connected through quadrature capacitors 34, 35, 36 and 37to the plates of the phase 1 inverters. High value resistors 38-, 40,41, 42 from a 13 supply to the plates, of the. phase shifting tubesprovide the DC. plate voltages.v Phase shifting control voltages are fedfrom the limiter cathode followers disposed in series with the secondarywindings of transformers 43, 44, 45 and 46to the grids of'the phaseshifter tubes. Signals, which represent simulated echoes when the phaseshifter circuit is associated with a sonar trainer, are fed to the gridsof'the phase, inverter tubes 25, 26, 27 and 28 through capacitor andresistance couplings 47, 48, 50 andSl, respectively, and also to theprimary windings of transformers 43, 44, 45 and 46. The plate resistanceof the phase shifters is controlled by the phase shifting modulatingvoltages placed on their grids from the limiter circuits in serieswiththe transformer secondaries. The value ofthe phase shifter plateresistance is, of course, limited. by cutoff bias ofthe tube for thenegativeswing and zerogrid H bias of the tube which is the maximumachieved voltage. on the positive swing. Phase shiftingcircuitsfollowing. this general form are capable of a maximum. phaseswing of 180 or plus and minus 90 providing the variable re sistance canvary from zero to infinity. Since this is not possible with the phaseshifter tube, less than this phase swing normally obtains. When thephase shifter tubes are acting in the above described manner as purevariable resistances their grids must be fed the same signal, equalminimum amplitude at the center phase position and increasing evenlywithphase rotation either way.

The plate circuit of each. phase shifter is capacity coupled to anisolating cathode follower, the cathode followers being numberedrespectively in the four channels from. left to right 52, 53,. 54 and55. This enhances stability of performance in the phase shifters andreduces the effect of. the output loading on their operation. Thecoupling capacitors are purposely kept small so that low frequencymodulating, components would be discriminated against.

It is understood that various modifications may be made in the design ofboth the limiter and phase shifting circuits, as above described, bypersons skilled in the art without departing from the principle andscope of the invention as defined in the following claims.

What is claimed is:

1. A phase shifting circuit comprising phase inverting means, a signalsource connected to said phase inverting means, a phase shifting tubehaving a plate, grid and cathode, the cathode of said tube beingconnected to one side of said phase inverting means, a quadraturecapacitor connected between the plate of saidphase shifting tube and theother side of said phase inverting means, a resistor connected to theplate of the phase shifting tube and adapted to apply a plate voltage tosaid tube, means for applying. the signal voltage provided by saidsignalsource to the grid of said phase shifting tube and means forapplying to the grid of said phase shifting tube a phase shiftingcontrol or modulating voltage.

2. A phase shifting circuit comprising phase inverting means, a signal.source connected to said phase inverting means, a phase shifting tubehaving a plate, grid and cathode, the cathode of saidrtube beingconnected to one side of said phase inverting means, a quadraturecapacitor connected, between the plate of said phase shifting tube andthe other side of said phase inverting means, a resistor connected tothe plate of the phase shifting tube and adapted to apply a platevoltage to said tube, a transformer having its primary connected to saidsignal source and its secondary connected. to the grid ofsaid phaseshifting tube and a source of phase shifting control voltage connectedin series with said secondary and adapted to apply a modulating voltageto said grid.

3. A phase shifting circuit as claimed in claim 1 wherein voltage phaseshifting and amplitude controlling means are inserted between said phaseinverting means and the grid of said phase shifting tube whereby thephase and amplitude of the voltage applied to said grid and said cathodeof the phase shifting tube are relatively adjustable.

4. A phase shifting circuit as claimed in claim 2 wherein a coupledcapacitor and shunt resistor is connected between said signal source andsaid phase inverting means whereby the phase and amplitude of thevoltage applied tothe grid and the cathode of the phase shifting tubeare relatively adjustable.

5. A phase shifting circuit as claimed in claim 2 wherein an isolatingcathode follower is connected to output of said phase shifting tube toprevent adverse loading effects on the performance thereof.

6. A phase shifting circuit as claimed in claim 2 wherein: a limitercircuit is connected between saidsource of phase shifting controlvoltage and said phaseshifting tube whereby the control voltage isprevented from having peak voltage swings beyond grid current andcut-off of the phase shifting tube.

References Cited in the file of this patent UNITED STATES PATENTS2,085,940 Armstrong July 6, 1937 2,266,541 Foster et a1 Dec. 16, 19412,454,426 Beckwith Nov. 23, 1948 2,513,809 Martin July 4, 1950 2,552,348Shapiro et a1. May 8, 1951 2,576,499 Bowes Nov. 27, 1951

